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Headphones on a stand


Headphones are made in a range of different audio reproduction quality capabilities. Headsets designed for telephone use typically cannot reproduce sound with the high fidelity of expensive units designed for music listening by audiophiles. Headphones that use cables typically have either a 1/4 inch (6.35mm) or 1/8 inch (3.5mm) phone jack for plugging the headphones into the audio source. As of 2015, most headphones are amplified by a headphone amplifier, either an integrated amplifier (e.g., in an iPod) or a standalone unit.


Brandes radio headphones, circa 1920.

Headphones originated from the earpiece, and were the only way to listen to electrical audio signals before amplifiers were developed. The first truly successful set was developed in 1910 by Nathaniel Baldwin, who made them by hand in his kitchen and sold them to the United States Navy.[3][4]

Some very sensitive headphones, such as those manufactured by Brandes around 1919, were commonly used for early radio work. These early headphones used moving iron drivers, with either single ended or balanced armatures. The requirement for high sensitivity meant that no damping was used, thus the sound quality was crude. These early models lacked padding, and often produced excessive clamping forces on the wearer's head. Their impedance varied; headphones used in telegraph and telephone work had an impedance of 75 ohms. Those used with early wireless radio had to be more sensitive and were made with more turns of finer wire. Impedance of 1000 to 2000 ohms was common, which suited both crystal sets and triode receivers.


In 1943, John C. Koss, an audiophile and jazz musician from Milwaukee, produced the first stereo headphones. Previously, headphones were used only by telephone and radio operators, and individuals in similar industries.





Wired headphones are attached to an audio source by a cable. The most common connectors are 6.35 mm (¼″) and 3.5 mm phone connectors. The larger 6.35 mm connector is more common on fixed location home or professional equipment. Sony introduced the smaller, and now widely used, 3.5 mm "minijack" stereo connector in 1979, adapting the older monophonic 3.5 mm connector for use with its Walkman portable stereo tape player. The 3.5 mm connector remains the most widely-used connector for portable application today. Adapters are available for converting between 6.35 mm and 3.5 mm devices.

Electrical characteristics




The impedance of headphones is of concern because of the output limitations of amplifiers. A modern pair of headphones is driven by an amplifier, with lower impedance headphones presenting a larger load. Amplifiers are not ideal; they also have some output impedance that limits the amount of power they can provide. In order to ensure an even frequency response, adequate damping factor, and undistorted sound, an amplifier should have an output impedance less than 1/8 that of the headphones it is driving (and ideally, as low as possible). If output impedance is large compared to the impedance of the headphones, significantly higher distortion will be present.[5] Therefore, lower impedance headphones will tend to be louder and more efficient, but will also demand a more capable amplifier. Higher impedance headphones will be more tolerant of amplifier limitations, but will produce less volume for a given output level.

Historically, many headphones had relatively high impedance, often over 500 ohms in order to operate well with high impedance tube amplifiers. In contrast, modern transistor amplifiers can have very low output impedance, enabling lower impedance headphones. Unfortunately, this means that older audio amplifiers or stereos often produce poor quality output on some modern, low impedance headphones. In this case, an external headphone amplifier may be beneficial.


Sensitivity is a measure of how effectively an earpiece converts an incoming electrical signal into an audible sound. It thus indicates how loud the headphones will be for a given electrical drive level. It can be measured in decibels of sound pressure level per milliwatt (dB (SPL)/mW) or decibels of sound pressure level per volt (dB (SPL) / V).[6] Unfortunately, both definitions are widely used, often interchangeably. As the output voltage (but not power) of a headphone amplifier is essentially constant for most common headphones, dB/mW is often more useful if converted into dB/V using Ohm's Law:

dB (SPL)/V = dB (SPL)/mW - 10*\log10{\frac{Impedance}{1000}}

Alternatively, online calculators can be used.[7] Once the sensitivity per volt is known, the maximum volume for a pair of headphones can be easily calculated from the maximum amplifier output voltage. For example, for a headphone with a sensitivity of 100 dB (SPL)/V, an amplifier with an output of 1 root-mean-square (RMS) voltage will produce a maximum volume of 100 dB.






Circumaural headphones have large pads that surround the outer ear.



A pair of supra-aural headphones.


Open or closed back


Open-back headphones have the back of the earcups open. This leaks more sound out of the headphone and also lets more ambient sounds into the headphone, but gives a more natural or speaker-like sound and more spacious "soundstage"[further explanation needed] - the perception of distance from the source.

Closed-back (or sealed) styles have the back of the earcups closed. They usually block some of the ambient noise, but have a smaller soundstage, giving the wearer a perception that the sound is coming from within their head. Closed-back headphones tend to be able to produce stronger low frequencies than open-back headphones.

Semi-open headphones, have a design that can be considered as a compromise between open-back headphones and closed-back headphones. This may imply that the result combines all the positive properties of both designs. Some[who?] believe the term "semi-open" is purely there for marketing purposes. There is no exact definition for the term semi-open headphone. Where the open-back approach has hardly any measure to block sound at the outer side of the diaphragm and the closed-back approach really has a closed chamber at the outer side of the diaphragm, a semi-open headphone can have a chamber to partially block sound while letting some sound through via openings or vents.

Ear-fitting headphones

Earbuds/earphones sit in the outer ear


Earphones (popularly called "earbuds" in recent years) are very small headphones that are fitted directly in the outer ear, facing but not inserted in the ear canal. Earphones are portable and convenient, but many people consider them to be uncomfortable and prone to falling out.[10] They provide hardly any acoustic isolation and leave room for ambient noise to seep in; users may turn up the volume dangerously high to compensate, at the risk of causing hearing loss.[10][11] On the other hand, they let the user be better aware of their surroundings. Since the early days of the transistor radio, earphones have commonly been bundled with personal music devices. They are sold at times with foam pads for comfort.

In-ear headphones


In-ear headphones, also known as in-ear monitors (IEMs) or canalphones,[12] are small headphones with similar portability to earbuds that are inserted in the ear canal itself. IEMs are higher-quality in-ear headphones and are used by audio engineers and musicians as well as audiophiles.

Because in-ear headphones engage the ear canal, they can be less prone to falling out, and they block out much environmental noise. Lack of sound from the environment can be a problem when sound is a necessary cue for safety or other reasons, as when walking, driving, or riding near or in vehicular traffic.



A typical example of a headset used for voice chats.


Telephone headsets

Sony Ericsson Cordless bluetooth headset



Ambient noise reduction

Among different types of headphones, in-ears are good for noise isolation.


Passive noise isolation is essentially using the body of the earphone, either over or in the ear, as a passive earplug that simply blocks out sound. The headphone types that provide most attenuation are in-ear canal headphones and closed-back headphones, both circumaural and supra aural. Open-back and earbud headphones provide some passive noise isolation, but much less than the others. Typical closed-back headphones block 8 to 12 dB, and in-ears anywhere from 10 to 15 dB. Some models have been specifically designed for drummers, with the aim to be able to monitor the recorded sound while shutting out the sound coming directly from the drums at the same time as much as possible. Such headphones claim to reduce ambient noise by around 25 dB.


Transducer technology

Various types of transducer are used to convert electrical signals to sound in headphones.


A typical moving-coil headphone transducer



Electrostatic loudspeaker diagram



Electrostatic headphones require a voltage source generating 100 V to over 1 kV, and are on the user's head. They do not need to deliver significant electric current, which limits the electrical hazard to the wearer in case of fault.


An electret driver functions along the same electromechanical means as an electrostatic driver. However the electret driver has a permanent charge built into it, where electrostatics have the charge applied to the driver by an external generator. Electret and electrostatic headphones are relatively uncommon. Electrets are also typically cheaper and lower in technical capability and fidelity than electrostatics.



An orthodynamic driver consists of a relatively large membrane which contains an embedded wire pattern. This membrane is suspended between two sets of permanent, oppositely aligned, magnets. When current is passed through the wires which are embedded in the membrane, the magnetic field produced by the current reacts with the field caused by the permanent magnets and induces movement in the membrane, producing sound.

Balanced armature

Balanced armature transducer with armature balanced and exerting no force on diaphragm


The JH Audio JH16 custom in-ear monitor utilizes 8 balanced armatures in a triple crossover configuration (4 low/2 mid/2 high). Multiple balanced armatures are often used to provide a higher fidelity sound.


Today they are typically used only in in-ear headphones and hearing aids, where their diminutive size is a major advantage. They generally are limited at the extremes of the hearing spectrum (e.g. below 20 Hz and above 16 kHz) and require a better seal than other types of drivers to deliver their full potential. Higher-end models may employ multiple armature drivers, dividing the frequency ranges between them using a passive crossover network. A few combine an armature driver with a small moving-coil driver for increased bass output.


Thermoacoustic technology

The thermoacoustic effect generates sound from the audio frequency Joule heating of the conductor, an effect which is not magnetic and does not vibrate the speaker. In 2013 a carbon nanotube thin-yarn earphone based on the thermoacoustic mechanism was demonstrated by a research group in Tsinghua University.[13] The as-produced CNT thin yarn earphone has a working element called CNT thin yarn thermoacoustic chip. Such a chip is composed of a layer of CNT thin yarn array supported by the silicon wafer, and periodic grooves with certain depth are made on the wafer by micro-fabrication methods to suppress the heat leakage from the CNT yarn to the substrate.[citation needed]

Other transducer technologies



Benefits and limitations

Two Sony MDR-V6 headphones; one folded for travel




Binaural recordings use a different microphone technique to encode direction directly as phase, with very little amplitude difference below 2 kHz, often using a dummy head, and can produce a surprisingly lifelike spatial impression through headphones. Commercial recordings almost always use stereo recording, rather than binaural, because loudspeaker listening has been more popular than headphone listening.



Dangers and volume solutions


The government of France has imposed[19] a limit on all music players sold in the country:[19] they must not be capable of producing more than 100dBA (the threshold of hearing damage during extended listening is 80 dB, and the threshold of pain, or theoretically of immediate hearing loss, is 130 dB).[20] Motorcycle and other power-sport riders benefit by wearing foam earplugs when legal to do so to avoid excessive road, engine, and wind noise, but their ability to hear music and intercom speech is enhanced when doing so. The ear can normally detect 1-billionth of an atmosphere of sound pressure level,[21] hence it is incredibly sensitive. At very high sound pressure levels, muscles in the ear tighten the tympanic membrane and this leads to a small change in the geometry of the ossicles and stirrup that results in lower transfer of force to the oval window of the inner ear (the acoustic reflex).[22]

Some studies have found somewhat increased risks for temporary hearing damage from listening to music during strenuous exercise, compared to when listening at rest.[23] A Finnish study[24] recommended that exercisers should set their headphone volumes to half of their normal loudness and only use them for half an hour.


The usual way of limiting sound volume on devices driving headphones is by limiting output power. This has the additional undesirable effect of being dependent of the efficiency of the headphones; a device producing the maximum allowed power may not produce adequate volume in low-efficiency high-quality headphones, while possibly reaching dangerous levels in very efficient ones.[citation needed]

See also


  1. 1.0 1.1 "earphone". Retrieved 4 January 2014.<templatestyles src="Module:Citation/CS1/styles.css"></templatestyles>
  2. Stanley R. Alten Audio Basics Cengage 2011 ISBN 0-495-91356-1 page 63
  3. "Howeth: Chapter XI (1963)". earlyradiohistory.us. Retrieved 21 July 2015.<templatestyles src="Module:Citation/CS1/styles.css"></templatestyles>
  5. Siau, John. "The "0-Ohm" Headphone Amplifier" (PDF). Retrieved 26 June 2012.<templatestyles src="Module:Citation/CS1/styles.css"></templatestyles>
  6. http://gilmore2.chem.northwestern.edu/tech/dbohn1_tech.htm
  7. "Headphone Sensitivity & Efficiency Calculator". Retrieved 22 November 2014.<templatestyles src="Module:Citation/CS1/styles.css"></templatestyles>
  9. "Understanding Earphone/Headphone Specifications". Shure Customer Help. Shure. Retrieved 30 December 2012.<templatestyles src="Module:Citation/CS1/styles.css"></templatestyles>
  10. 10.0 10.1 10.2 Ha, Peter (26 April 2010). "Earbud Review: Best Headphones for Price, Hearing Safety - TIME". TIME.com. Retrieved 21 July 2015.<templatestyles src="Module:Citation/CS1/styles.css"></templatestyles>
  11. "Output Levels of Commercially Available Portable Compact Dis... : Ear and Hearing". LWW. Retrieved 21 July 2015.<templatestyles src="Module:Citation/CS1/styles.css"></templatestyles>
  12. In-ear monitors are referred to as "earbuds" by some manufacturers. The box for the "J2" from jbuds describes the product as noise isolating soft silicone earbuds with the latest cutting edge In-Ear design. Also, Koss' The Plug is "a stereo earbud" that "features ... a tubular port structure that is inserted on a soft expandable cushion into the ear canal." Skullcandy also sells "in-ear earbuds" - http://www.skullcandy.com/shop/skin/frontend/default/skullcandy_main-v3/images/ninjistics/in-ear.png
  13. Yang Wei; Xiaoyang Lin; Kaili Jiang; Peng Liu; Qunqing Li; Shoushan Fan (2013). "Thermoacoustic Chips with Carbon Nanotube Thin Yarn Arrays". Nano Letters. 13 (10): 4795–801. doi:10.1021/nl402408j. PMID 24041369.<templatestyles src="Module:Citation/CS1/styles.css"></templatestyles>
  14. cnet reviews: Headphone Buying Guide "Even the flimsiest, cheap headphones routinely boast extremely low bass-response performance—15 or 20Hz—but almost always sound lightweight and bright."
  15. United States Department of Labor. Occupational Safety & Health Administration. Computer Workstation. Checklist. Accessed February 2, 2009.
  16. "Causes of Hearing Loss in Adults". asha.org. Retrieved 21 July 2015.<templatestyles src="Module:Citation/CS1/styles.css"></templatestyles>
  17. "Noise-Induced Hearing Loss". nih.gov. Retrieved 21 July 2015.<templatestyles src="Module:Citation/CS1/styles.css"></templatestyles>
  18. William W. Clark. "Five Myths in Assessing the Effects of Noise on Hearing". AudiologyOnline. Retrieved 21 July 2015.<templatestyles src="Module:Citation/CS1/styles.css"></templatestyles>
  19. 19.0 19.1 Europa.eu. Consumers: EU acts to limit health risks from exposure to noise from personal music players
  20. "Medical Information Search (Cochlea • FAQ)". Lookformedical.com. Retrieved 2013-09-06.<templatestyles src="Module:Citation/CS1/styles.css"></templatestyles>
  21. A standard threshold of hearing at 1000 Hz for the human ear is 2 x 10−5 Pa (Marsh, Andrew (1999). "Human Ear and Hearing". Online Course on Acoustics. The School of Architecture and Fine Arts, The University of Western Australia. Retrieved 23 August 2010.<templatestyles src="Module:Citation/CS1/styles.css"></templatestyles>); Standard atmospheric pressure is 101,325 Pa. 2 x 10−5 / 100,000 = 0.2 x 10−9, a ratio of less than a billionth.
  22. "The Ear's Protective Mechanisms". gsu.edu. Retrieved 21 July 2015.<templatestyles src="Module:Citation/CS1/styles.css"></templatestyles>
  23. "Can Loud Noise during Exercise Damage my Hearing?". Healthy Hearing. Item 4. Retrieved 8 November 2014.CS1 maint: location (link)<templatestyles src="Module:Citation/CS1/styles.css"></templatestyles>
  25. Greenfield, Paige (25 June 2011). "Deaf to Danger: The Perils of Earbuds". ABC News. Retrieved 20 June 2013.<templatestyles src="Module:Citation/CS1/styles.css"></templatestyles>

External links